A conventional technique of identifying whether or not a modulated wave is a multicarrier wave based on a baseband signal extracted from the modulated wave is known. Further, a technique of changing a transmission capacity in accordance with transmission characteristics of an optical transmission path without changing a transceiver circuit is known.
Further, in recent years, modulation schemes such as Orthogonal Frequency Division Multiplexing (OFDM), for example, Discrete Multi-Tone modulation (DMT), Pulse Amplitude Modulation (PAM), and the like have been studied. Examples of the related art are Japanese Laid-open Patent Publication No. 2007-336078 and Japanese Laid-open Patent Publication No. 2008-167126.